This invention relates generally to positive-displacement pumps and, more particularly, to impeller shaft seals for such pumps.
Low pressure positive-displacement pumps often are used as sanitary pumps to pump fluid food products, such as catsup, mayonnaise, relish, soup and the like. In these applications, it is essential to continually move the fluid food products through the pump so that none of the products can collect within the pump and stagnate. Should stagnation occur, entire batches of food product could spoil, resulting in economic loss.
One type of pump often used in such sanitary applications is a dual-chamber, dual-lobe pump. Each lobe, or impeller, is driven by a drive shaft, which is sealed from the pump chamber by a two-part seal, comprising a rotary seal member mounted on the impeller, a stationary seal member surrounding the drive shaft, and a spring biasing the stationary seal member into engagement with the rotating seal member. Both of these seal members are conventionally circular and concentric with the drive shaft axis. These seal members and the housing define a confined peripheral pocket. Turbulence of the fluid product prevents it from collecting and stagnating in this pocket. Turbulence of a pumped fluid can be caused by cavitation, which is the result of supplying less fluid to the pumping chamber than the chamber can hold. However, cavitation results in reduced efficiency and ultimate pump damage due to resulting turbulence which causes severe fluid expansion impact to the surface of the pump parts. To counteract turbulence, pump manufacturers, such as applicant's assignee, have developed improved pump designs such as disclosed in U.S. Pat. No. 3,799,713--Cloots et al. However, reduced turbulence increases the aforementioned pumped fluid food product stagnation problem.
It is, therefore, an object of this invention to provide an improved shaft seal which reduces, or eliminates, the problem of collection and stagnation of pumped fluid food product in a sanitary pump in which turbulence is reduced or eliminated. It is a further object to provide a shaft seal which has reduced wear.